Recent work on sympathetic neurons indicates that their transmitter status is more complicated than the current textbook views; there is evidence for new transmitters, (e.g. purines, peptides), multiple-transmitter status, plasticity and graded expression. The long term objective is to investigate these complexities with a "microculture" method devised in this laboratory that permits an unusually direct study of each of these new complexities in single neurons co-cultured with appropriate target cells. Neurons dissociated from perinatal or adult ganglia of rats will be grown, one or a few at a time, on tiny islands of target cells (e.g. other neurons, cardiac or smooth myocytes); transmitter status is determined by stimulating the neuron and recording electrically from the neuron and its target cells, with use of appropriate drugs. The fine structure or immunocytochemistry can be then correlated directly with the function of this neuron. Specific aims: 1. With regard to the adrenergic-to-cholinergic transition, to investigate i) Retention of certain adrenergic properties. ii) Can the transition be reversed? iii) Are adult neurons back-labelled from a particular target tissue homogeneous in transmitter status and its transition(s)? iv) In a multiple-function neuron, is a single varicosity multiple in function? A single vesicle? 2. With regard to purinergic function(s) to invetigate i) The pharmacology of purinergic function; are there separate P1 and P2 -receptors? Uptake mechanism? ii) Investigate the storage mechanism(s) for secreted purine(s). Health relatedness. These new complexities of transmitter status are of general interest in neurobiology. A proper understanding of neuronal control of internal organs depends on an understanding of these complexities.